Simplify AllKeywords.

It's a verbose reinvention of a range type, and can be cut down a lot.

Author: nnethercote

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -22,7 +22,7 @@ use rustc_errors::{
 use rustc_session::errors::ExprParenthesesNeeded;
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::source_map::Spanned;
-use rustc_span::symbol::{AllKeywords, Ident, kw, sym};
+use rustc_span::symbol::{Ident, kw, sym, used_keywords};
 use rustc_span::{BytePos, DUMMY_SP, Span, SpanSnippetError, Symbol};
 use thin_vec::{ThinVec, thin_vec};
 use tracing::{debug, trace};
@@ -811,7 +811,7 @@ impl<'a> Parser<'a> {
             // so that it gets generated only when the diagnostic needs it.
             // Also, it is unlikely that this list is generated multiple times because the
             // parser halts after execution hits this path.
-            let all_keywords = AllKeywords::new().collect_used(|| prev_ident.span.edition());
+            let all_keywords = used_keywords(|| prev_ident.span.edition());
 
             // Otherwise, check the previous token with all the keywords as possible candidates.
             // This handles code like `Struct Human;` and `While a < b {}`.

compiler/rustc_span/src/symbol.rs

@@ -2682,41 +2682,19 @@ impl Ident {
     }
 }
 
-/// An iterator over all the keywords in Rust.
-#[derive(Copy, Clone)]
-pub struct AllKeywords {
-    curr_idx: u32,
-    end_idx: u32,
-}
-
-impl AllKeywords {
-    /// Initialize a new iterator over all the keywords.
-    ///
-    /// *Note:* Please update this if a new keyword is added beyond the current
-    /// range.
-    pub fn new() -> Self {
-        AllKeywords { curr_idx: kw::Empty.as_u32(), end_idx: kw::Yeet.as_u32() }
-    }
-
-    /// Collect all the keywords in a given edition into a vector.
-    pub fn collect_used(&self, edition: impl Copy + FnOnce() -> Edition) -> Vec<Symbol> {
-        self.filter(|&keyword| {
-            keyword.is_used_keyword_always() || keyword.is_used_keyword_conditional(edition)
+/// Collect all the keywords in a given edition into a vector.
+///
+/// *Note:* Please update this if a new keyword is added beyond the current
+/// range.
+pub fn used_keywords(edition: impl Copy + FnOnce() -> Edition) -> Vec<Symbol> {
+    (kw::Empty.as_u32()..kw::Yeet.as_u32())
+        .filter_map(|kw| {
+            let kw = Symbol::new(kw);
+            if kw.is_used_keyword_always() || kw.is_used_keyword_conditional(edition) {
+                Some(kw)
+            } else {
+                None
+            }
         })
         .collect()
-    }
-}
-
-impl Iterator for AllKeywords {
-    type Item = Symbol;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        if self.curr_idx <= self.end_idx {
-            let keyword = Symbol::new(self.curr_idx);
-            self.curr_idx += 1;
-            Some(keyword)
-        } else {
-            None
-        }
-    }
 }